reformat or skip?

Lately, it seems like my MacBook Pro (mid 2009) has been running really slowly when I'm using the finder, and whenever I am using Chrome and/or Firefox with Flash enabled chat sites, it seems to have issues with the video stopping completely and/or stopping and resuming constantly. When I took my mac to the genius bar last week (to find out why my iPod Touch 5th gen had so many issues with crashing, restarting on its own, and syncing), the technician said my computer had a lot of 3rd party stuff that might cause issues with iTunes, so, when I finally bought an external HD, I wondered if it would be better to reformat my mac's internal HD and reinstall the OS... I am in the process of a time machine backup to my 500 GB time machine drive, and I'm wondering if I should go ahead with reformatting the internal drive, and then installing 10.6.8? I was told that I shouldn't upgrade my machine beyond snow leopard if I only have 4 GB ram installed, but, if I do a reinstall of 10.6.8, should I even consider installing a newer version of Mac OS X (since 10.6 is now unsupported by many developers)? thanks!